The egalitarian friendship between black abolitionist Douglass and President Lincoln during the American Civil War proved a role model for the new America.

Douglass remarked, "In his company I was never in any way reminded of my humble origin, or of my unpopular colour."

James Watt, Josiah Wedgwood, Erasmus Darwin and Joseph Priestley

These four young men became friends when they met in the English Midlands in the 1760s.

They founded the Lunar Society and spurred each other into making discoveries that kickstarted the Industrial Revolution; steam engines (Watt), the discovery of oxygen (Priestley), mass production (Wedgwood's pottery), evolutionary theory (Darwin, followed later by his grandson Charles).

Michael Collins and Harry Boland

Collins and Boland helped bring the British to the Treaty table but the best friends ended up on opposite sides during the ensuing Civil War.

When anti-Treatyite Boland was shot in August 1922, a devastated Collins wrote to Kitty Kiernan that "my mind went to him lying dead there and I thought of the times together".

Thelma and Louise

Alright. They're not real people: but the on-screen sacrifice of Susan Sarandon and Geena Davis moved the phrase 'till death do us part' beyond the realm of romantic love.

Ben Affleck and Matt Damon

The partnership of Affleck and Damon might not be as earth-moving as that of, say, DNA scientists Crick and Watson (unless you are a person who believes Good Will Hunting is the Best Film Ever Made).

But their close relationship, eclipsing even Affleck's penchant for famous Jennifers, is the prototype for the 'bromance' phenomenon of recent popular culture.